1. Field of the Invention
This invention relates to thermoplastic molding compositions based on copolyether-ester polymer blends and more particularly to blends of high molecular weight copolyether-esters with polyoxymethylene, to give blends of improved physical properties.
2. Relation to the Prior Art
Thermoplastic molding resins based on polyoxymethylene blends which contain at least 50% oxymethylene polymer are well known in the art, for example, U.S. Pat. Nos. 3,795,715; 3,696,171; 3,476,832; German Pat. No. 2,449,343; Can. Pat. No. 844,683. Applicant's copending application Ser. No. 749,220 now U.S. Pat. No. 4,117,033, discloses oxymethylene polymers which contain up to about 5% of low molecular weight copolyether-ester resins to give blends with improved melt processability. Also known are polyoxymethylene/aliphatic polyester block polymers (U.S. Pat. No. 3,580,973).
It is also known to modify the properties of polyester molding compositions based on linear saturated polyesters of aromatic dicarboxylic acids and optionally small amounts of aliphatic dicarboxylic acids, by addition of up to 25% of a polyacetal (U.S. Pat. No. 3,595,937). Brown et al. (U.S. Pat. No. 3,907,926) teach that copolyether-ester resin blends which contain between about 5 and 200 parts of poly(butylene terephthalate) per 100 parts of the copolyether-ester resin show improved physical properties, particularly high initial modulus and good low temperature impact strength and flexibility, compared with the copolyether-ester resins themselves. Blends of copolyether-ester resins with less than 50% polyoxymethylene have not previously been described.